Re: Question About DxeDriver load process

[Rafael Machado <rafaelrodrigues.machado@gmail.com>]

Hi Andrew

Thanks a lot for the perfectly detailed explanation!
Amazing!

Thanks and Regards
Rafael R. Machado

Em sex, 27 de jul de 2018 às 19:14, Andrew Fish <afish@apple.com> escreveu:

> Rafael,
>
> Since it is useful to also understand this when you are bringing up a
> platform....
>
> SEC generally contains the hardware reset vector. SEC hands off to the PEI
> Core. Generally there is some build magic to help SEC find the PEI Core.
> Worst case you can walk the BFV (Boot Firmware Volume) and find it.
>
> SEC hands the PEI Core the EFI_SEC_PEI_HAND_OFF structure. This is how the
> PEI Core knows about stack, heap, and the location of the BFV to find PEIMs
>
> https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Pi/PiPeiCis.h#L967
>
> The PEI Core has a PPI Notify Callback for
> gEfiPeiFirmwareVolumeInfoPpiGuid, and  gEfiPeiFirmwareVolumeInfo2PpiGuid to
> discover new FVs.
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Pei/FwVol/FwVol.c#L547
>
> PEI Code writes hobs, EFI_HOB_TYPE_FV and EFI_HOB_TYPE_FV3, to help DXE
> discover FVs.
>
> When the DXE Core is started it will call FwVolBlockDriverInit() and  all
> the EFI_HOB_TYPE_FV, and optionally pick up the authentication status from
> EFI_HOB_TYPE_FV3, will get processed.
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/FwVolBlock/FwVolBlock.c#L625
>
> via calling ProduceFVBProtocolOnBuffer(). ProduceFVBProtocolOnBuffer() can
> also be called gBS->ProcessFirmwareVolume().
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/FwVolBlock/FwVolBlock.c#L452
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/FwVolBlock/FwVolBlock.c#L687
>
> Loading drivers from the FV is the job of the DXE Dispatcher. The DXE
> Dispatcher has protocol notify event on gEfiFirmwareVolume2ProtocolGuid
> that will get the executables in the Dispatch list, mDiscoveredList.
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/Dispatcher/Dispatcher.c#L1193
>
> So adding a gEfiFirmwareVolume2ProtocolGuid driver, or calling
> gBS->ProcessFirmwareVolume() is how you would make an FV show up that was
> not listed in the HOBs.
>
> In the DXE Phase security is handle by gBS->LoadImage() and it uses
> gEfiSecurity2ArchProtocolGuid and gEfiSecurityArchProtocolGuid to validate
> the image. This makes sense as a signed EFI PE/COFF image has the signature
> in the PE/COFF image, so you have to start the PE/COFF loading process to
> verify that signature.  gEfiSecurity2ArchProtocolGuid lets you build
> security policy based on the location of the driver.
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/Image/Image.c#L1041
>
> When the Dispatcher runs of things to Dispatch it returns and the DXE Core
> calls the BDS to process platform Boot Device Selection.
>
> https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c#L550
>
> After BDS starts the only way to run code from an FV would be to call
> gDS->Dispatcher(). Likely you would call gDS->ProcessFirmwareVolume() and
> then  gDS->Dispatcher(). To speed boot it is not uncommon to have multiple
> FVs. For example you could have an FV that contained all the setup
> resources and only call gDS->ProcessFirmwareVolume() on that FV if the user
> hit the Setup hot key.
>
> Thanks,
>
> Andrew Fish
>
> PS For x86 (0xFFFFFFF0 reset vector) and any other architectures that have
> the reset vector at the end there is a special file name in the FV called
> gEfiFirmwareVolumeTopFileGuid that tells the FV creation tools to put that
> file at the very end of the FV, so the end of that file would end up at the
> reset vector location.
>
>
> > On Jul 27, 2018, at 11:12 AM, Rafael Machado <
> rafaelrodrigues.machado@gmail.com> wrote:
> >
> > Hi everyone
> >
> > I have a question.
> > Let's suppose I have a BIOS with several FV regions. Between these FV
> there
> > is one that is empty.
> >
> > My question is:
> > In case I get this BIOS and inject a dxe driver at this FV. Would it be
> > executed, or there are specific FVs that are considered as containers to
> > executable code avoiding other FVs content to be executed?
> >
> > In case the answer comes with some code examples from edk2 tree it would
> be
> > amazing :)
> >
> > Thanks and Regards
> > Rafael
> > _______________________________________________
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> > edk2-devel@lists.01.org
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>
>